Module signal 

Exit codes, signals and job control.

The SIGPIPE regression

The Rust runtime sets SIGPIPE to SIG_IGN before main runs, because a Rust program would rather see EPIPE from a write than die. That setting is inherited across exec, so a child launched by prk run starts with SIGPIPE ignored – which is not what it was written to expect.

Concretely, prk run -- yes | head -1 hangs forever: head exits, the pipe closes, and yes never receives the signal that would stop it. Every program in a pipeline that relies on SIGPIPE to know when to stop is affected, which is most of them.

The fix is restore_default_dispositions, called from pre_exec immediately before the image is replaced. Its regression test is tests/unix_exec.rs::yes_piped_into_head_terminates_rather_than_hanging.

The signal mask

Blocked signals are also inherited across exec, and a blocked signal is not something the child can discover or undo before it matters. prk does not block anything itself, but it may have been started by something that did, so the mask is cleared rather than assumed empty.

Constants

SIGINT

SIGINT, the signal Ctrl-C sends.

SIGNAL_EXIT_BASE

The offset a shell adds to a signal number to form an exit status.

SIGPIPE

SIGPIPE, which the Rust runtime ignores and which must be restored.

SIGTERM

SIGTERM, the default kill signal.

Functions

child_exit_status

Maps a child’s outcome to the status prk should exit with.

exit_status_for_signal

The exit status a shell reports for a process killed by a signal.

restore_default_dispositions

Restores the signal state a freshly-started program expects.